Galvanic anode assembly



Sept. 18, 1951 H. A. ROBINSON GALVANIC ANODE ASSEMBLY 2 Sheets-Sheet 1 Filed Jan. 26, 1949 IN V EN T 0R. Harv/0C4. Robinson BY A TTORNE 2 3 Sept. 18, 1951 H. A. ROBINSON GALVANIC ANODE ASSEMBLY 2 Sheets-Sheet 2 Filed Jan. 26, 1949 INVENTOK Haro/a A. rQo/hson Patented Sept. 18, 1951 GALVANIC ANODE ASSEMBLY Harold A. Robinson, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich" a corporation of Delaware Application January 26, 1949, Serial No. 72,877 3 Claims. (01.204-197) This invention relates to an improved galvanic anode assembly for use in the cathodic protection of metal vessels.

In one form of cathodic protection of metal vessels against corrosion by natural waters, a consumable anode of galvanically active metal anodic to the vessel is suspended in the water and connected electrically to the vessel wall. The resulting flow of current maintains the vessel cathodic to the medium and minimizes its corrosion. A diificulty arises, however, in the protection of water heaters and water softeners operating on highly mineralized waters of low electrical resistance. In such waters, the anode develops more current than is needed, shortening its useful life unnecessarily, producing objectionable gassing, and occasionally imparting an undesirable color or odor to the water.

This excessive current flow may be prevented by inserting a resistor of suitable value in the circuit between the anode and the metal vessel. Such a resistor is usually housed in a special adapter fitting which also holds the anode in position and connects it electrically to the vessel. Prior adapters have, however, been expensiveand poorly suited to quantity production, particularly with respect to the way in which the resistor had to be installed. They were further disadvantageous in that they provided no means for re-, moving the built-in resistance from the circuit without destroying the whole adapter assembly, no matter how desirable such removal may have become due to changes in operating conditions.

It is therefore a principal object of the present invention to provide an improved resistor-type anode and adapter assembly which may be inexpensively produced and in which the resistor is easily installed. Another objectis to provide an adapter assembly in which there is adjustable means for optionally shorting-out the resistor whenever circumstances demand.

These objects are attained in the invention by the use of a metal plug adapter having a recess in its base and a body of galvanically active metal one end of which is held by the plug and fits into it to a depth insufficient to rest on the end of the recess, the active metal being insulated electrically from the plug. A cartridge resistor and an electrically conducting compressibly elastic member, such as a metal spring, are connected electrically in series and placed within the plug recess in such position between the end or the recess and the end of the galvanic body that the elastic member rests against one of the two ends and presses the resistor against the other of the ends. The assembly may also include an adjustable screw or other means operable through the head of the plug for shortening out the cartridge resistor.

The invention may be explained in detail with reference to the accompanying drawings in which Fig. 1 is a vertical section through an adapter assembly according to the invention;

Fig. 2 is a fragmentary cutaway view of a water tank with the assembly of Fig. 1 installed to protect the tank against corrosion;

Fig. 3 is a vertical section through an alterna tive form of assembly according to the invention;

Fig. 4 is a vertical section through another form of assembly according to the invention; and

Fig. 5 is an enlarged detail of the screw, spring, and cartridge resistor in Fig. 4.

In Fig. 1, the adapter comprises a hexagonalhead brass or other metal plug 6 provided with external pipe threads 1 and having a cylindrical axial recess 8 bored in its base. Integral with the plug is an extension 9 in the form of a cylindrical tube coaxial with the recess 8, the walls of the tube being sufliciently thin to be deformable for crimping. Within the recess. and of substantially smaller diameter, is a tubular spacer ll) of wood or other electrical insulating material.

A galvanic anode in the form of a cylindrical magnesium rod I I provided with a steel wire core l2 fits into the extension 8 to seat against the spacer l0. As shown, the rod H is reduced in diameter at its upper end in order to enter the extension 9 loosely. A sleeve of waterproof flexible electrical insulating material l3, such as a rubber tube, is slipped over the end of the rod ll so as to be interposed between the latter and the extension 9. The metal of the extension is crimped against the sleeve l3, providing a watertight joint and holding the rod ll firmly in the assembly.

Within the plug recess inside the spacer III are a cartridge resistor l4 and a steel or other electrically conducting spring IS. The resistor and spring are electrically in series, with the spring resting against the end of the anode rod II in firm contact with it and pressing the resistor against the end of the recess 8 in electrical contact with the plug. Consequently, in the assembly illustrated, the galvanic anode H is held by the plug 8 but is connected electrically to it only through the resistor It.

For use in domestic hot water tanks. theplug 6 is usually of a size to fit a or 1" I. P. S. tank opening, the anode is a 0.8 to 13-inch magnesium-alloy rod 3 to 4 feet long, and the resistor is in the range of 5 to ohms.

In Fig. 2, the assembly of Fig. 1 is shown in use in the cathodic protection of galvanized steel domestic water heater tank l6 having the usual inlet dip-pipe I1 and an outlet opening 18. The assembly is best installed through an auxiliary threadedopening 19 in the top of the tank. The plug 6 is screwed firmly into the opening so that the anode rod II is held suspended in the tank.

Fig. 3 is illustrative of an alternative formv of the assembly of Fig. 1 in whichthe tubular connected electrically to the plug and the other spacer is omitted. The plug recess Bis provided with a smaller central recess or socket 120 to.. receive the cartridge resistor-14. .One endoi-a 1 spring 2| is soldered to an end of the resistor,-

while the other end of the spring fits into a small socket 22 bored in the end of the core l2 of the rod Ii. 7 I The adapter assembly df Figs. 4 and 5 is simila r. to "that of Fig. 1, but includes means for optionally shorting out; the resistance between theanodeand .the' plug. As shown particue larly in Fig. 5, the cartridge resistor indicated generallyas 23 comprises a ceramic or other, insulating tube 2t around-Which is wound'an e1ec' tric r'esistanc'e wire '25, the wire being covered with a coating of insulating cement 26. At theibottdm or anode end the cartridge terminates in a metal caps2'lhaving asharp point which bears against the'core Wire E2 of the anode H. At the upper orplug end the cartridge is providedwith aii outside. metal band 28. The resistance wire 25 is connected electrically and mechanically to b'oththe cap 22. and the band :7."

use that thelatter constitute electrically iso lated end elements-which .are connected through a resistor. Inside 'the ceramic tube 24 of the to the ihe'tal'body, and adjustable means mounti ed on-a'nd operablethrough the head of the plug for optionally shorting out the resistor. 2. In a galvanic anode assembly for insertion through the wall of a metal vessel to be protected cathodically and comprising a metal plug havinga recess in the base thereof, a body of galcartridge isa. brass or other electrically conduct.-

ing pin 29 which is soldered to the cap 2? but is'insulate'd from the band'28. A steel'coil spring 30 is soldered to the band 28, being thus in se ides with the resistor. The other end of the spring seats on abrass. screw 3i provided with a sharp conical pointflas shown. This screw extends through a threaded hole 32 in the head of the plug 6 whichis coaxial with the resistor 23;. V V

When'the screw 3i is adjusted'so that its point does not touchthe resistor core 29, the spring 30 presses the. resistor against the end of the anode it. Under theseconditions, the anode H andp'lug Bare connected only through the resistance element However, when the screw 3| is tightened to bear against the brass core 29', the plug'fi and anode ii are directly conriect'ed: through the core, the resistance element being shorted out. In this construction it is thus possible to eliminatethe resistance, or include it in circuit, as often as may be desired, simply by turning the screw 3i, without having to remove the assembly from service.

While the assembly of the inventionis usually employed in the cathodic protection offerrous metal structures, it may be used in the protection of any corrodible metahprovided only that the rod H is formed of galvanically active metal anodic toi-the metal .to be protected. The anodic metal is usually zinc, aluminum, r'n'agn'esium, or a magnesium-base alloy, the latter twovbeing comprehended by the term magnesiurn' meta as used herein.

vanically active metal one end of which fits into the :plug to a depth insufficient to restion the end "of therece'ss;and-electrical insulation in terposed between the plug and themetal body, the combination ef a' cartridge resistor within the. plug .recess,,. one end of which is connected electrically .to the plug and the other touthe. metal body,.and an adjustable metal screw ex: ter'iding'lthro'ugh the plugin: electrical contact therewith in position optionally to short out the having a recess;v iii-the base thereoia bodymi galvanically active: m'etal one-rend of which fits into the plug to ai-depth, insufficient ,to -rest on r the end of the recess, a'nctelectrical insulation; interposed between the plugv and-the ;met,al body; the combination of an electrically conducting spring anda-nelong'ated cartridge resistorwithin the phig' recess, the cartridge comprising sepa' rate --conductiveend element's interconnected electrically. through a resistor and a conductive core-extending axially through the cartridge and connected electrically to only one of the end ele-i mentsgth'e' spring havingone' end in electrical contact-with the end of the recess and the other end bcaringiaga'inst the end element of the car-5 tr'idge which'is not-connected'to the core to press the other end of the cartridge against the body. of galvanic metal, and anadjustable screWfQXj tending through-the head of the metal plug in electrical contact. therewith. and in positionope tionall y to contact the-core of the cartridge refile of this patent-t PATEN'rsf UNITED Y' STATE Number -Name Date ."1,960,'3137 Rabezza'na May-29, 1933i 2,301,570 Nowosielski Nov. 10, 19 12 2,486,871. Osterheld NOV. 1,194

' OTHER REFERENCES V fThe Use of Magnesium Anodes for the .Pre

vention of Corrosion} in Water Heaters-andI-Iot Water Tanks, by Dow Chemical Co.

' 1947) i Fig. fl of supplement. a 

